It has been known that a typical operation device usable in a fader and the like has a structure for adjusting an operation load applied to a movable portion (see, for instance, Patent Literatures 1 and 2).
The operation device of Patent Literature 1 includes: a movable member slidable along a guide shaft; and an adjuster configured to adjust a sliding torque of the movable member. The adjuster includes: a square C-shaped spring provided to a lower end of the movable member; a buffer provided to an inner wall of one of a pair of free ends of the spring; and an adjustment screw connecting the pair of free ends of the spring to each other. In this structure, a distance between the free ends of the spring is adjusted by rotating the adjustment screw, thereby adjusting a friction force between the buffer and the guide shaft, resulting in an adjustment of the sliding torque of the movable member.
The operation device of Patent Literature 2 includes a slide member slidable along a first shaft. The slide member is provided with a plate spring configured to press the slide member onto the first shaft and a cam configured to adjust a pressing force of the plate spring according to a rotation of the cam. In this structure, the pressing force of the plate spring is adjusted according to the rotation of the cam to adjust a pressing force of the slide member applied to the first shaft, resulting in an adjustment of a sliding torque of the slide member.